OBJECTIVES: An effective measurement tool is required to assess the economic effects of acute ischemic stroke (AIS) imaging interventions and to determine how the magnitude of AIS-attributable impairment changes over time so that these may be incorporated into economic analyses.  The modified Rankin scale (mRS) is the most prevalently used measure of AIS outcomes however it has generated skepticism, concern and confusion regarding the results of stroke outcome studies.  This study assesses all clinimetric properties of the mRS and outlines improvement opportunities. METHODS: The mRS was analyzed using a set of clinimetric assessment instruments including the Bombardier sensibility assessment tool and Beaton responsiveness guidelines.  Each clinimetric domain was evaluated, namely, measure development; item generation; measure administration; sensibility; reliability; validity; and responsiveness. RESULTS: The mRS displayed many shortcomings including: 1) vague definition of concept measured; 2) lack of item generation rigor; 3) compromised face validity; 4) no evidence of validity and reliability among AIS patients; and 5) inadequate study of responsiveness due to arbitrary choices of clinically important differences for comparison scales. CONCLUSIONS: The mRS is a flawed instrument for estimating AIS outcomes.  Minimally, high quality, adequately powered de novo assessments of its validity, reliability and responsiveness should be undertaken.  Preferably, a new AIS outcome measure to measure should be developed by following the detailed recommendations within each of the clinimetric properties sections of this assessment.  This ideal AIS outcome measure could be applied to AIS outcome studies resulting in a facilitation, rather than obfuscation, of efforts to reduce the burden of AIS.